With Empoli, Antonini made his debut in European competitions on 20 September 2007, in a UEFA Cup first-round game against Zürich, also scoring a penalty. Despite the team being relegated, he had an extremely good season, also showing versatility when coach Alberto Malesani started to employ him as a full-back. Return to Milan (2008–2013) On 9 June 2008, Antonini was brought back by Milan and included in their squad for €2.75 million plus €150,000 other fee, in a pure player swap. (Antonini and Abate to Milan for a total fee of €4.75 million, Pozzi and Marzoratti to Empoli for a total fee of €4.75 million) In his first season with the Rossoneri, he did not get much playing time though, making only 11 league appearances. For the 2009–10 campaign, Milan signed a new head coach Leonardo, who initially did not seem to take Antonini into much consideration. However, as the season progressed, injuries to first-string players such as Zambrotta and Jankulovski prompted the Brazilian to put him in the line-up. Antonini seized his chance and earned Leonardo's trust by constantly performing well. His valuable performances also persuaded the club to offer him a contract extension until 2014, which was signed on 11 February 2010. He finished his second year at Milan on a high, scoring his first goal for the Rossoneri in the last match of the season, a home game against Juventus, on 15 May 2010. When new coach Massimiliano Allegri was appointed in the summer of 2010, he kept Antonini at the left-back position and Luca was a regular in the starting XI for the whole of the 2010–11 season, helping Milan win their 18th Scudetto. He continued to be a regular for the 2011–12 season, where Milan disappointingly finished second to Juventus but managed to win the Supercoppa Italiana in the summer of 2011. Genoa (2013–2015) At the start of the 2013–14 season, Antonini left Milan to join Genoa as part of a deal which saw midfielder Valter Birsa move the other way. He made 26 appearances in Serie A, scoring two goals, in his first season with the Grifone. The following season, he made just seven appearances and was then released by the club. Ascoli and Livorno loan (2015–2016) Antonini joined Serie B side Ascoli on 4 September 2015. On 1 February 2016, he moved to Livorno on a half-season loan. Return to Prato (2016) On